1. Field of the Invention
This invention relates to a liquid crystal display and processes for manufacturing and driving thereof. In particular, it relates to a liquid crystal display which can be readily manufactured, has excellent properties for an angle of visibility and can give a quick response, as well as processes for manufacturing and driving thereof.
2. Description of the Related Art
In a twisted nematic (hereinafter referred to as xe2x80x9cTNxe2x80x9d) type of liquid crystal display which has been widely used, its display status is gradually changed from xe2x80x9cwhitexe2x80x9d where a voltage is not applied and thus liquid crystal molecules are parallel to the surface of a substrate, to xe2x80x9cblackxe2x80x9d by varying an applied voltage to change the direction of the director of the liquid crystal molecules in the direction depending on the electric field.
The TN type of liquid crystal display, however, has a narrow angle of visibility due to the unique behavior of the liquid crystal molecules by applying a voltage; it is particularly marked in the rising-up direction of the liquid crystal molecules in half tone display.
The TN type of liquid crystal display does not respond sufficiently quickly to be suitable for displaying animation.
JP-A 4-261522 and JP-A 6-43461 have suggested techniques for improving properties for an angle of visibility of a liquid crystal display. In the techniques, a homeotropically-oriented liquid crystal cell is prepared. It is placed between two polarizing plates located in a manner that their polarization axes are perpendicular to each other. As shown in FIG. 7, using a common electrode 32 having an opening 34, a nonuniform field is generated to divide each pixel into at least two liquid crystal domains for improving the properties for an angle of visibility. JP-A 4-261522 has disclosed a process for achieving a high contrast by controlling a direction of an orientation of liquid crystal molecules when a voltage is applied. As described in JP-A 6-43461, properties for an angle of visibility in the xe2x80x9cblackxe2x80x9d status, may be, if necessary, improved by using an optical compensator. Furthermore, JP-A 6-43461 has disclosed that each pixel may be divided into at least two domains by a nonuniform field in a TN-oriented cell as well as a homeotropically-oriented liquid crystal cell for improving their properties for an angle of visibility.
These techniques, however, require xe2x80x9cfine processing steps such as a photoresist step for the common electrode 32xe2x80x9d which is not necessary for manufacturing a usual TN type of liquid crystal display and advanced superposition of the upper and the lower substrates 23, 33. The problem is particularly marked for an active matrix type of liquid crystal display employing switching elements such as TFT. Specifically, in a usual active matrix type of liquid crystal display, active elements such as thin-film diodes are fabricated on one transparent substrate. Fine processing steps such as a photoresist step are, therefore, required only on one substrate, while the other substrate on the side of the electrode usually called as xe2x80x9ca common electrodexe2x80x9d does not require fine processing and has only an electrode on its overall surface. On the other hand, the display of the above-mentioned prior art requires fine processing steps such as a photoresist step for xe2x80x9ca common electrodexe2x80x9d which does not need to be finely processed, leading to increase of the number of steps and necessity for advanced superposing the upper and the lower substrates 23, 33.
In addition, as shown in FIG. 7, the display of the prior art described above has a disadvantage that since it does not have an electrode in the region of the opening 34, the region may not be provided with a sufficient field for liquid crystal molecules to adequately respond to a voltage applied to the electrode 32. Furthermore, the display of the prior art has a disadvantage that it does not give a quick response.
JP-A 9-105041 has disclosed another technique for improving properties for angle of visibility, in which in one substrate liquid crystal molecules are oriented substantially vertical to the substrate surface, while in the other substrate the molecules are oriented substantially parallel to the substrate surface; and each pixel is divided into a plurality of regions different in a rising (lying for a vertical orientation part) direction of liquid crystal molecules to compensate the properties for angle of visibility in these regions each other and thus to enlarge the angle of visibility.
The technique disclosed in JP-A 9-105041 requires additional complicated processes such as a photoresist process for dividing each pixel into a plurality of regions and a polarized radiation process via a mask. FIG. 9 shows an example in which a pixel is divided into two regions. To make the orientation directions of the liquid crystals different by 180xc2x0 each other in rubbing, there must be added a series of processes, i.e., rubbing the surface of the substrate in one direction 41 while covering a half of the pixel region with, e.g., a resist mask, removing the resist mask, and then rubbing the substrate in the opposite direction while covering the remaining exposed half of the pixel region with a resist mask. When employing polarized radiation, there must be added a series of processes, i.e., radiating polarized light on a half of the pixel from an oblique direction using a similar mask and then radiating polarized light on the remaining unexposed half from an oblique direction different from the first direction by 180xc2x0.
In addition, JP-A 7-84254 and JP-A 7-49509 have disclosed techniques for improving properties of angle of visibility and a response speed of a liquid crystal display. In these techniques, a bend-oriented liquid crystal cell is prepared, which is then placed between two polarizing plates whose polarization axes are perpendicular to each other. Thus, such a display utilizes the action that the orientations near upper and lower substrates compensate their birefringence each other, to improve its properties for angle of visibility, as shown in FIG. 10. This approach has an advantage of quick response. As described in JP-A 7-84254, the display employs an optical compensator if necessary, to improve properties for angle of visibility in black. Furthermore, JP-A 9-120059 has disclosed a technique that after voltage application, prepolymer is polymerized with UV radiation to stabilize bend orientation, for preventing the bend orientation from being converted into spray orientation.
The display utilizing bend orientation exhibits quicker response and is improved in properties for angle of visibility, compared with a conventional TN-oriented display. It, however, has regions in which gradation inversion occurs, resulting in inadequate properties for angle of visibility.
An approach that a pixel is divided by providing an opening in the electrode on one substrate (JP-A 4-2615522 and JP-A 6-43461) cannot be applied to bend orientation in which the tilt directions of both upper and lower substrates should be controlled.
An objective of this invention is to solve the problems in the prior art, i.e., to provide a liquid crystal display which exhibits high contrast and quick response and has excellent properties for an angle visibility.
Another objective of this invention is to provide a process for readily manufacturing the above liquid crystal display without increase of troublesome processes such as a photoresist step.
A further objective of this invention is to provide a driving process by which the liquid crystal display can fully exhibit its good features such as high contrast, quick response and excellent properties for an angle of visibility.
This invention provides a liquid crystal display comprising a liquid crystal layer between two substrates each of which has an electrode, wherein the liquid crystal layer concomitantly has at least two micro-regions, and the electrode on one or both of the substrates have an opening, in the region of which there is provided a second electrode for controlling the initial orientation of the liquid crystal.
This invention also provides a liquid crystal display comprising a liquid crystal layer between two substrates each of which has an electrode, wherein the liquid crystal layer concomitantly has at least two micro-regions, and one or both of the substrates have the electrode on which there is provided a second electrode insulated from the said electrode for controlling the initial orientation of the liquid crystal.
This invention further provides a process for manufacturing a liquid crystal display comprising a liquid crystal layer between two substrates each of which has an electrode, wherein the liquid crystal layer concomitantly has at least two micro-regions, and the electrode on one or both of the substrates have an opening, in the region of which there is provided a second electrode for controlling the initial orientation of the liquid crystal, comprising the steps of injecting liquid crystal into an empty panel which has two substrates each of which has an electrode, and in which the electrode on one or both of the substrates have an opening where there is provided second electrode for controlling the initial orientation of the liquid crystal; and applying, between the second electrode and a counter electrode thereto, a voltage equal to or higher than that applied between the electrode having the opening and a counter electrode thereto to control the initial orientation of the liquid crystal.
This invention further provides a process for manufacturing a liquid crystal display comprising a liquid crystal layer between two substrates each of which has an electrode, wherein the liquid crystal layer concomitantly has at least two micro-regions, and one or both of the substrates have the electrode on which there is provided a second electrode insulated from the said electrode for controlling the initial orientation of the liquid crystal, comprising the steps of injecting liquid crystal into an empty panel which has two substrates each of which has an electrode, and in which one or both of the substrates have the electrode on which there is provided second electrode insulated from the said electrode for controlling the initial orientation of the liquid crystal; and applying, between the second electrode and a counter electrode thereto, a voltage equal to or higher than that applied between the electrode having the second electrode and a counter electrode thereto to control the initial orientation of the liquid crystal.
This invention further provides a process for driving a liquid crystal display comprising a liquid crystal layer between two substrates each of which has an electrode, wherein the liquid crystal layer concomitantly has at least two micro-regions, and the electrode on one or both of the substrates have an opening, in the region of which there is provided a second electrode for controlling the initial orientation of the liquid crystal, comprising the step of applying, between the second electrode and a counter electrode thereto, a voltage equal to or higher than that applied between the electrode having the opening and a counter electrode thereto.
This invention further provides a process for driving a liquid crystal display comprising a liquid crystal layer between two substrates each of which has an electrode, wherein the liquid crystal layer concomitantly has at least two micro-regions, and one or both of the substrates have the electrode on which there is provided a second electrode insulated from the said electrode for controlling the initial orientation of the liquid crystal, comprising the step of applying, between the second electrode and a counter electrode thereto, a voltage equal to or higher than that applied between the electrode having the second electrode and a counter electrode thereto.
In the above liquid crystal display of this invention, the liquid crystal layer can be divided into at least two micro-regions by applying a voltage between the second electrode and the counter electrode thereto to control the initial orientation of the liquid crystal. Thus, a display with high contrast, quick response and excellent properties for an angle of visibility such as a wide angle of visibility can be provided without increase of troublesome manufacturing steps such as a photoresist step.
The description, xe2x80x9cin the region of the openingxe2x80x9d herein means that the opening and the second electrode almost overlap in a front view of the liquid crystal display; it does not necessarily mean that the second electrode is at the same position as the opening in a section view. In other words, the opening and the second electrode may be in xe2x80x9cthe same layerxe2x80x9d as shown in FIG. 3 as well as in xe2x80x9cdifferent layersxe2x80x9d via an insulating film as shown in FIG. 1. Herein, the description, xe2x80x9cthe opening and the second electrode is in the same layerxe2x80x9d means that there is provided the second electrode 25 electrically insulated from a pixel electrode 22, in the opening 24 formed in the pixel electrode 22, for example, as shown in FIG. 3. The description, xe2x80x9cthe initial orientation of the liquid crystalxe2x80x9d means the orientation of the liquid crystal at the beginning of driving in its broad sense, and may also mean the initial orientation during manufacturing the panel.
According to the invention, there can be provided a liquid crystal display with high contrast, quick response and excellent properties for an angle of visibility. Such a liquid crystal display may be used to display an excellent image. The liquid crystal display can be readily manufactured at a reduced cost, without increase of troublesome steps such as a photoresist step.